[clang] [CLANG] Enable alignas after GNU attributes (PR #133107)

[Aaron Ballman via cfe-commits]

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@@ -71,6 +71,12 @@ namespace test_misplacement {
 [[]] union union_attr2; //expected-error{{misplaced attributes}}
 [[]] enum  E2 { }; //expected-error{{misplaced attributes}}
 }
+struct S1 { __attribute__((deprecated)) alignas(16) int x; }; // expected-none
+class C1 { __attribute__((deprecated)) alignas(16) int x; }; // expected-none
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AaronBallman wrote:

I'd like to see a test case like which shows the various combinations of orders we can handle (no need to test `struct` and `class` separately as those follow the same code paths).
```
class C {
  __attribute__(()) [[]] alignas(int) int x;
  __attribute__(()) alignas(int) [[]] int y;
  [[]] __attribute__(()) alignas(int) int z;
  alignas(int) [[]] __attribute__(()) int a;
};
```
We should also be sure to test this in C23 mode to make sure we get the same behavior in C as well as in C++.

https://github.com/llvm/llvm-project/pull/133107